1. Field of the Invention
This invention generally relates to an imaging apparatus or a solid-state imaging apparatus which can be used in, for example, a video camera system. This invention particularly relates to an imaging apparatus or a solid-state imaging apparatus having a function of suppressing a flicker in images represented by a video signal. Furthermore, this invention relates to a video-signal processing circuit for suppressing a flicker which can be used in an imaging apparatus.
2. Description of the Related Art
In NTSC, a field period which equals the reciprocal of a field frequency is {fraction (1/60)} sec, that is, 16.6 ms. Light generated by a fluorescent lamp powered by 50-Hz AC power iteratively goes on and off at a period of 10 ms. In some cases, an object whose image is taken by an NTSC video camera is illuminated with a fluorescent lamp powered by 50-Hz AC power. In these cases, pictures represented by the output signal of the video camera flicker at a period of 50 ms (a 3-field-corresponding period) which equals the least common multiple of 16.6 ms and 10 ms.
A known flicker correcting system processes a video signal field by field. The known flicker correcting system tends to be insufficiently effective to a flicker which occurs in only a portion of a 1-field area.
It is a first object of this invention to provide an imaging apparatus able to effectively suppress a flicker which occurs in only a portion of a 1-field area or a 1-frame area.
It is a second object of this invention to provide a video-signal processing circuit able to effectively suppress a flicker which occurs in only a portion of a 1-field area or a 1-frame area.
A first aspect of this invention provides an imaging apparatus comprising first means for generating at least one picture division signal; second means for dividing every picture represented by a video signal into at least first and second areas in response to the picture division signal generated by the first means; third means for detecting a mean luminance of the first area and a mean luminance of the second area; fourth means for correcting a flicker in the first area to derive a first correction-resultant area in response to the mean luminance of the first area which is detected by the third means; fifth means for correcting a flicker in the second area to derive a second correction-resultant area in response to the mean luminance of the second area which is detected by the third means; and sixth means for combining the first correction-resultant area and the second correction-resultant area into a correction-resultant picture.
A second aspect of this invention is based on the first aspect thereof, and provides an imaging apparatus wherein the third means comprises means for detecting the mean luminance of the first and the mean luminance of the second areas in response to the picture division signal generated by the first means.
A third aspect of this invention is based on the first aspect thereof, and provides an imaging apparatus wherein the fourth means comprises a first video amplifier for amplifying the video signal corresponding to the first area at a first gain, and means for controlling the first gain in response to the mean luminance of the first area which is detected by the third means, and wherein the fifth means comprises a second video amplifier for amplifying the video signal corresponding to the second area at a second gain, and means for controlling the second gain in response to the mean luminance of the second area which is detected by the third means.
A fourth aspect of this invention is based on the first aspect thereof, and provides an imaging apparatus wherein the first means comprises means for setting the picture division signal to make inconspicuous a boundary between the first correction-resultant area and the second correction-resultant area in the correction-resultant picture.
A fifth aspect of this invention is based on the first aspect thereof, and provides an imaging apparatus wherein the first means comprises means for setting the picture division signal to make movable a boundary between the first area and the second area.
A sixth aspect of this invention is based on the first aspect thereof, and provides an imaging apparatus wherein the fourth means and the fifth means comprise a common video amplifier for amplifying the video signal at a controllable gain, means for, when the video signal corresponds to the first area, controlling the gain of the video amplifier in response to the mean luminance of the first area which is detected by the third means, and means for, when the video signal corresponds to the second area, controlling the gain of the video amplifier in response to the mean luminance of the second area which is detected by the third means.
A seventh aspect of this invention is based on the first aspect thereof, and provides an imaging apparatus further comprising seventh means for deciding whether or not a flicker is present in the first area in response to the mean luminance of the first area which is detected by the third means; eighth means for deciding whether or not a flicker is present in the second area in response to the mean luminance of the second area which is detected by the third means; and ninth means for controlling the picture division signal generated by the first means to move a boundary between the first area and the second area in response to a result of the decision by the seventh means and a result of the decision by the eighth means.
An eighth aspect of this invention provides a video-signal processing circuit comprising first means for dividing every picture represented by a video signal into first and second areas; second means for processing the video signal which corresponds to the first area to correct a flicker in the first area; and third means for processing the video signal which corresponds to the second area to correct a flicker in the second area.
A ninth aspect of this invention is based on the eighth aspect thereof, and provides a video-signal processing circuit further comprising fourth means for changing a boundary between the first area and the second area.
A tenth aspect of this invention is based on the eighth aspect thereof, and provides a video-signal processing circuit further comprising fourth means for detecting whether or not a flicker is present in the first area; fifth means for detecting whether or not a flicker is present in the second area; and sixth means for changing a boundary between the first area and the second area in response to a result of the detection by the fourth means and a result of the detection by the fifth means.